gistfile1.js

// Create a new object
ajax = new XMLHttpRequest(); 

// Try to open a API resource that won't return a 200 or 201
ajax.open("GET", "https://api.flattr.com/rest/v2/user", false); 
ajax.send();

// The response
ajax.responseText;
// "{"error":"unauthorized","error_description":"You are unauthorized to access the resource","error_uri":"http:\/\/developers.flattr.net\/api\/"}"
ajax.status;
// 401